ECHINODERMS, DOLLAR DOVES & PETRIFIED BISCUITS

ECHINODERMS, DOLLAR DOVES & PETRIFIED BISCUITS

Echinoderms (Gr. ‘Hedgehog Skin’) comprise a large variety of sea creatures characterised (mostly) by radial symmetry. In a nutshell a creature with radial (as opposed to bilateral) symmetry can be divided into equal portions from the centre, like a cake. It has no left or right side and no definable front or back. It is multidirectional from the centre, where the mouth is located. It obviously has a distinct upper side and an underside, but that has no bearing on this form of symmetry.

Within the family of radially symmetrical animals, echinoderms (starfish, sand dollars and sea urchins) are unique in having five-point radial symmetry. These are the creatures you are most likely to come across in Abaco. There are two particular aspects of dollars and biscuits that merit a closer look (made more difficult by me stupidly taking photos of white things on a white background).

DOLLAR DOVES

I’m sure all Bahamians know or are aware of at least one version of the famous ‘Sand Dollar’ poem, in which the various characteristics of the test (the skeleton of the creature) are given religious significance. One verse of the poem may be puzzling: “Now break the centre open And here you will release The five white doves awaiting To spread good will and peace”.

The Sand Dollar Legend

A few years back, Senior Granddaughter was looking at some Abaco sand dollars I’d given her for her growing collection of shells. She picked one up, shook it and it rattled. She said a friend at school had told her that a rattling sand dollar has ‘doves’ inside it, and asked if we could break it open and see. I’ve learnt that it is useless to argue with her – she has the tenacity of a trial lawyer – so we did. This is what we found.

Sand Dollar with a spiky interior like a white cave with stalagmites and stalagtites

Five white doves (in fact, the separated parts of the creature’s feeding apparatus)

Two broken pieces showing where the doves are centrally located

A regrettably poor photo of a single dove

The image below, from Pinterest, shows the ‘mouth’ with its dove-parts intact, in an arrangement called ‘Aristotle’s Lantern‘, a five-sided globular structure that supports the mouth and jaws of an echinoderm.

PETRIFIED BISCUITS

In common parlance ‘petrified’ is an extreme version of ‘terrified’. Literally, it means ‘turned to stone’ (L. petrus, a rock). It is descriptive of a state of fossilisation, where an animal skeleton or dead wood or plant matter turns over aeons into stone. Senior GD (a most inquisitive girl) followed up on the doves research after discovering a box containing random stones and fossils. She found these two items:

Fossilised sea biscuits

A closer look at the pair of rocks

The undersides of the fossils above – looking like stones but with some tell-tale small holes

A close-up of the pale biscuit

Sea biscuits on the beach at Delphi – familiar white skeletons (‘tests’) but not yet fossils

A ‘modern’ non-Jurassic Abaco sea biscuit in close-up

FUN FACT

Florida has an unofficial but proposed State Fossil, the ‘Sea Biscuit (Eocene Age)’. I didn’t know it before, but it turns out that more than 40 US States have State Fossils. Whatever next? State Bacteria? State Viruses?

SO HOW OLD MIGHT A PETRIFIED BISCUIT BE?

The fossil biscuits I have looked at, from Florida to Madagascar (see small image above), are said to come from three specific historic epochs – from the oldest, Jurassic (145m – 201m years ago), to Eocene (34m – 56m) and Pleistocene (0.01m – 2.6m).

HOW DOES THAT HELP ANYBODY? BE MORE PRECISE

By all means. Here is an excellent Geochart that gives an idea of the time span. A Jurassic sea biscuit would be more than 145m years old. This chart also helpfully helps avoid confusion with the Eon Era Period Epoch ordering.

All photos ‘in-house’ except the Delphi biscuits, Clare Latimer; & the single biscuit Rhonda Pearce; Sand Dollar poem on Postcard, Dexter Press; the Geochart was in my ‘useful chart photos’ folder but I can’t now find the source. I did try.

Thanks so much. This is perfect for sharing with our family, who love finding these sea biscuits and sand dollars on the beach. Life just gets more complicated, and more interesting, as we dig for improved understanding and knowledge of our natural world.

Truly excellent post, RH. So interesting! I have picked up sand dollars and heard the rattle, but never knew anything about the mouth and the doves. I’m grateful to your Senior Granddaughter for her curiosity and you, for pointing this all out. The fossilized sea biscuits are fascinating, and the Abaco sea biscuits are beautiful.